Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A system and method for network selection procedures for simultaneous
network connectivity through multiple accesses comprises obtaining stored
and registered PLMNs, determining whether PLMNs are both stored PLMN for
access technology type Ai and registered PLMN, when no PLMNs are both,
performing PLMN selection using a standard procedure, when only one PLMN
is both, determining whether the PLMN satisfies a condition, and when the
PLMN satisfies the condition, attempting to connect to the PLMN, and when
more than one PLMN is both, creating a set of PLMNs, selecting one PLMN
that satisfies the condition, from the set PLMN, attempting to connect to
the selected PLMN, and when attempting to connect fails, removing the
selected PLMN from the set, and selecting another PLMN. In one aspect,
the PLMN that minimizes changes is selected. In one aspect, the PLMN that
provides access to a larger number of access technologies is selected.

Claims:

1. A method for network selection procedures for simultaneous network
connectivity through multiple accesses, comprising steps of: obtaining,
on a user equipment having a CPU, stored public land mobile networks
(PLMNs) and registered PLMNs; determining whether one or more PLMNs are
both a stored PLMN for access technology type Ai and a registered PLMN;
when no PLMNs are both, performing PLMN selection for Ai using a standard
procedure; when only one PLMN is both, performing steps of: determining
whether the one PLMN satisfies a condition; when the one PLMN satisfies
the condition, attempting to connect to the one PLMN; and when more than
one PLMN is both, performing steps of: creating a set of the more than
one PLMN; selecting one PLMN of the set of PLMNs, said selected one PLMN
satisfying the condition; attempting to connect to the selected one PLMN;
and when attempting to connect fails, removing the selected one PLMN from
the set, and selecting another PLMN from the set.

2. The method according to claim 1, wherein the stored PLMNs are stored
on one of a Subscriber Identity Module (SIM) and a USIM.

3. The method according to claim 1, wherein the step of selecting further
comprises selecting the PLMN that minimizes changes.

4. The method according to claim 1, wherein the step of selecting further
comprises selecting the PLMN that provides access to a larger number of
access technologies.

5. A computer readable storage medium storing a program of instructions
executable by a machine to perform a method for network selection
procedures for simultaneous network connectivity through multiple
accesses, comprising: obtaining stored public land mobile networks
(PLMNs) and registered PLMNs; determining whether one or more PLMNs are
both a stored PLMN for access technology type Ai and a registered PLMN;
when no PLMNs are both, performing PLMN selection for Ai using a standard
procedure; when only one PLMN is both, performing steps of determining
whether the one PLMN satisfies a condition; when the one PLMN satisfies
the condition, attempting to connect to the one PLMN; and when more than
one PLMN is both, performing steps of: creating a set of the more than
one PLMN: selecting one PLMN of the set of PLMN, said selected one PLMN
satisfying the condition; attempting to connect to the selected one PLMN;
and when attempting to connect fails, removing the selected one PLMN from
the set, and selecting another PLMN from the set.

6. The computer readable storage medium according to claim 5, wherein the
stored PLMNs are stored on one of a Subscriber Identity Module (SIM) and
a USIM.

7. The computer readable storage medium according to claim 5, wherein
selecting further comprises selecting the PLMN that minimizes changes.

8. The computer readable storage medium according to claim 5, wherein
selecting further comprises selecting the PLMN that provides access to a
larger number of access technologies.

9. A system for network selection procedures for simultaneous network
connectivity through multiple accesses, comprising: a User Equipment (UE)
having a Subscriber Identity Module having a public land mobile networks
(PLMN) selection list, said UE registered to one or more PLMNs; and a
module operable to obtain stored PLMNs and registered PLMNs, to determine
whether one or more PLMNs are both a stored PLMN for access technology
type Ai and a registered PLMN, when no PLMNs are both, to perform PLMN
selection for Ai using a standard procedure, when only one PLMN is both,
to determine whether the one PLMN satisfies a condition, and when the one
PLMN satisfies the condition, to attempt to connect to the one PLMN, and
when more than one PLMN is both, to create a set of the more than one
PLMN, to select one PLMN of the set of PLMNs, said selected one PLMN
satisfying the condition, to attempt to connect to the selected one PLMN,
and when attempting to connect fails, to remove the selected one PLMN
from the set, and select another PLMN from the set.

10. The system according to claim 9, wherein to select one PLMN of the
set of PLMN further comprises selecting the PLMN that minimizes changes.

11. The system according to claim 9, wherein to select one PLMN of the
set of PLMN further comprises selecting the PLMN that provides access to
a larger number of access technologies.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and claims priority to U.S.
Provisional Application Ser. No. 61/294,859 filed on Jan. 14, 2010, the
entire contents and disclosure of which is incorporated herein by
reference.

FIELD OF THE INVENTION

[0002] This invention relates Public Land Mobile Network (PLMN) selection,
cellular networks, wireless networks, 3rd Generation Partnership
Project (3GPP) and Interworking-Wireless Local Area Networks (I-WLAN).
The present invention further relates generally to a (PLMN) selection
mechanism that allows multi-interface terminals to be simultaneously
connected to multiple access technologies with a minimum number of
registered PLMNs while maximizing the network connectivity.

BACKGROUND OF THE INVENTION

[0003] Terminals perform PLMN selection for each access technology as if
it were the only access technology the terminal is capable of connecting
to; this selection is not influenced by the fact that the terminal has a
multi-interface capability. There are existing standards specifications
defining PLMN selection procedures for 3GPP accesses, and TS 22.011 (v.
8.9.0), 3GPP, Technical Specification Group Services and Systems Aspects,
Service Accessibility (Release 9) specifies: "As consequence, the
multi-mode terminal when entering 3GPP mode of operation shall act as if
it were a 3GPP only UE [user equipment] which had just been switched-on.
Similarly, when leaving the 3GPP mode of operation the multimode terminal
shall act as if it were a 3GPP only UE which had just been switched-off".

[0004] Simultaneous connectivity over a 3GPP and a non-3GPP access is
supported in current specifications (see TS 23.402 (v.9.3.0) 3GPP
Technical Specification Group Services and System Aspects; Architecture
enhancements for non-3GPP accesses). PLMN selection for 3GPP and non-3GPP
accesses is performed in an independent manner (e.g., PLMN selection for
3GPP access [TS 22.011 (v.9.3.0) 3GPP Technical Specification Group
Services and System Aspects; Architecture enhancements for non-3GPP
accesses] and PLMN selection of I-WLAN [TS 23.234 (v.9.0.0) 3GPP
Technical Specification Group Services and System Aspects; 3GPP system to
Wireless Local Area Network (WLAN) interworking; System description and
TS 24.234 (v. 8.3.0), 3GPP, Technical Specification Group Core Network
and Terminals, 3GPP System to Wireless Local Area Network (WLAN)
Interworking; WLAN User Equipment (WLAN UE) to network protocols (Stage
3)]. There is no shared information between PLMN selection procedures for
3GPP and non-3GPP accesses. Instead, the list of preferred PLMNs for 3GPP
access is stored separately from the list of preferred PLMNs for non-3GPP
access, e.g., in USIM, PLMN record information is stored separately from
I-WLAN PLMN records (see TS 23.008 (v.9.1.0) 3GPP Technical Specification
Group Core Network and Terminals; Organization of subscriber data). The
last registered PLMN for 3GPP access is stored in the SIM/USIM as a
different record from the last registered PLMN for I-WLAN (see TS
23.008).

[0005] 3GPP also standardizes PLMN selection procedures for non-3GPP
access for I-WLAN (see TS 22.234, (v. 8.1.0), 3GPP, Technical
Specification Group Core Network and Terminals, Requirements on 3GPP
System to Wireless Local Area Network Interworking (Release 7) and TS
24.234). Separate from 3GPP accesses, there is no statement saying that
PLMN selection procedures for I-WLAN do not depend on the terminal having
multi-mode capabilities. The procedures defined, however, do not link
PLMN selection procedures for I-WLAN with PLMN selection procedures for
3GPP accesses.

[0006] Therefore, with current standards, PLMN selection procedures for
I-WLAN and PLMN selection procedures for 3GPP accesses are performed in
an independent manner. It is then possible for a multi-mode UE to connect
to different PLMNs over different accesses, for example, one for 3GPP
access and a different one for non-3GPP accesses. In such scenarios, flow
mobility among access networks may be limited due to the fact that
network policies can only be applied within an operator's domain.

[0007] PLMN selection procedures have been defined independently for each
access technology type, so that the PLMN selected on an access technology
type cannot influence the PLMN selected on a different access technology
type. Simultaneous connectivity over different 3GPP accesses is not
supported in current specifications. 3GPP PLMN selection procedures are
only defined when the UE is connected to only one 3GPP access at a time.
A preferred PLMN list can be access type specific, meaning that the list
of preferred PLMNs for access type i may be different from the list of
preferred PLMNs for access type j.

[0008] However, when the network sends policies to the UE to steer traffic
from one access network to another, e.g., Internet offload to WLAN or IP
flow mobility, such policies can only take effect among access networks
that belong to the same PLMN (or equivalent PLMN). This makes network
controlled mobility (or steering of access) between access technologies
difficult. In other words, it is not possible for operators to offload
traffic from their networks from one access technology type to another,
if these types are not connected on the UE to the same operator.

[0009] Accordingly, a multi-interface terminal selects PLMN for each
access type (each interface may be associated with a different access
type) in an independent manner, i.e., the fact that a PLMN has been
selected for a particular access type is not taken into account in the
PLMN selection of other access types. If the terminal is capable of
transmitting simultaneously over multiple interfaces, this independent
selection process may result in the terminal being simultaneously
connected to multiple PLMNs. In such a case, an operator cannot offload
traffic from one access type to another, as operator's policies can only
be applied within its own domain (i.e. within the same PLMN). For
example, if a terminal is connected to OP1 over 3GPP access and OP2 over
WLAN, OP1 cannot offload traffic to WLAN, as this would mean the traffic
would be offloaded to a different operator. Traffic offload to alternate
access is becoming very important for cellular operators as bandwidth
hungry data applications are growing.

[0010] Thus a generalized PLMN selection mechanism that considers
multiple-interface capability and network policy is needed to better
manage the flow mobility. Having generalized procedures of PLMN selection
for multi-interface terminals will allow operators to better manage the
flows across access networks through network policies.

SUMMARY OF THE INVENTION

[0011] An inventive generalized PLMN selection mechanism that allows
multi-interface terminals to be simultaneously connected to multiple
access technologies with a minimum number of registered PLMNs while
maximizing the network connectivity is presented. The novel technique is
coordinated with the knowledge of other interfaces and network policies,
and generalizes the solution, tries to minimize the number of PLMNs that
can be simultaneously connected to and thus allows operators to better
manage their traffic over different network types.

[0012] A method for network selection procedures for simultaneous network
connectivity through multiple accesses is presented. The method comprises
steps of obtaining, on a UE having a CPU, stored PLMNs and registered
PLMNs, determining whether one or more PLMNs are both a stored PLMN for
an access technology type Ai and a registered PLMN, when no PLMNs are
both, performing PLMN selection for access technology Ai using a standard
procedure, when only one PLMN is both, performing steps of determining
whether the one PLMN satisfies a condition, when the one PLMN satisfies
the condition, attempting to connect to the one PLMN, and when more than
one PLMN is both, performing steps of creating a set of the more than one
PLMN, selecting one PLMN of the set of PLMN, said selected one PLMN
satisfying the condition, attempting to connect to the selected one PLMN,
and when attempting to connect fails, removing the selected one PLMN from
the set, and selecting another PLMN from the set.

[0013] In one aspect, the stored PLMNs are stored on one of SIM/USIM. In
one aspect, selecting further comprises selecting the PLMN that minimizes
changes. In one aspect, selecting further comprises selecting the PLMN
that provides access to a larger number of access technologies.

[0014] A system for network selection procedures for simultaneous network
connectivity through multiple accesses comprises a UE having a SIM/USIM
having a PLMN selection list, said UE registered to one or more PLMNs,
and a module operable to obtain stored PLMNs and registered PLMNs, to
determine whether one or more PLMNs are both a stored PLMN for access
technology type Ai and a registered PLMN, when no PLMNs are both, to
perform PLMN selection for Ai using a standard procedure, when only one
PLMN is both, to determine whether the one PLMN satisfies a condition,
and when the one PLMN satisfies the condition, to attempt to connect to
the one PLMN, and when more than one PLMN is both, to create a set of the
more than one PLMN, to select one PLMN of the set of PLMN, said selected
one PLMN satisfying the condition, to attempt to connect to the selected
one PLMN, and when attempting to connect fails, to remove the selected
one PLMN from the set, and select another PLMN from the set.

[0015] In one aspect, to select one PLMN of the set of PLMN further
comprises selecting the PLMN that minimizes changes. In one aspect, to
select one PLMN of the set of PLMN further comprises selecting the PLMN
that provides access to a larger number of access technologies.

[0016] A computer readable storage medium storing a program of
instructions executable by a machine to perform one or more methods
described herein also may be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and other features, benefits, and advantages of the present
invention will become apparent by reference to the following figures,
with like reference numbers referring to like structures across the
views, wherein:

[0018] FIG. 1 shows a UE connected to multiple access networks of
different technology types using current standards.

[0030] UE: user equipment, including but not limited to a multi-mode
terminal, a mobile device, etc. User equipment has features including a
CPU.

[0031] Note that 3GPP has specified PLMN selection procedures for I-WLAN
only under the category of non-3GPP access. I-WLAN shall be considered as
one access technology for non-3GPP in this application.

[0032] A mechanism is presented to coordinate PLMN selection over
different access (3GPP and non-3GPP, or different 3GPP accesses) when the
UE is simultaneously connected through the different accesses. The number
of accesses to which the UE is simultaneously connected is not important.
In practice, such number will be limited by interference or UE
capabilities. Coordination of PLMN selection among different accesses can
be set as a configuration parameter. The home operator or the user can
set such configuration parameter.

[0033] When a new interface of access technology Ai powers up or it
recovers from loss of coverage, the UE shall try to connect to a PLMN
that meets the following requirements. The PLMN selection procedure shall
be able to use information already stored in the SIM/USIM card related to
PLMN selection, i.e., PLMN list per access technology. The PLMN selection
procedure shall be able to store and use information about last
registered PLMN for access technology type. As discussed above, current
3GPP standards only specify how to store in the SIM/USIM a single last
registered PLMN for 3GPP access and I-WLAN last registered PLMN. Using
the inventive technology, the UE shall be simultaneously connected to the
smallest number possible of PLMNs, while maintaining stability. The
number of PLMN re-selections over already connected accesses shall be
minimized. Home operator PLMN selection policies shall be taken into
account. PLMN selection policies may indicate a list of access technology
types for which PLMN re-selection shall not be attempted.

[0035]FIG. 4 is a flow diagram of the inventive method. In step S1,
obtain {PLMNi}, that is, obtain a list of PLMNIDs including the last
registered PLMNID for which there is an entry in the PLMN list stored in
the SIM/USIM for access technology Ai. In step S2, obtain {PLMNn}, that
is, a list of PLMNIDs containing PLMNIDs the UE is currently registered
with through different access technology types.

[0036] In step S3, obtain the set {PLMNin} as the set of PLMNIDs that
results from the intersection between {PLMNi} and {PLMNn}. If {PLMNin} is
the empty set (S4=YES), in step S5, the UE shall perform PLMN selection
for access technology Ai as if it were the only access technology the UE
were capable to connect to; this is performed by standard procedures.
After step S5, the process ends.

[0037] Otherwise, if {PLMNin} is NOT NULL (S4=NO), in step S6 the UE shall
obtain desired PLMNIDs from the {PLMNin} set obtained in step S3. These
desired PLMNIDs are selected PLMNIDs that provide connectivity through
the largest number of access technology types that satisfy a particular
condition. This condition could be empty, for example, select a PLMNID
that provides connectivity to the largest number of access technology
types with no condition. Alternatively, the operator could add a
condition related to location, for example, select a PLMNID that provides
connectivity to the largest number of access technology types and it is
allowed to connect at a particular location.

[0038] If there is only one PLMNID that satisfies this particular
condition (S7=YES), then, in step S8, this PLMNID is selected and the UE
attempts to connect to the PLMN of this selected PLMNID.

[0039] Otherwise, if there is more than one PLMNID that satisfies the
condition (S7=NO), in step S9, one PLMNID is selected as follows. The UE
shall first give priority to those PLMNs that are already registered with
and provide access to the largest number of already connected access
technology types. Second, it shall give priority to the PLMNs that have
the highest priority in the PLMN list stored in the UE for access
technology Ai.

[0040] After one PLMNID is selected, if the UE tries and successfully
connects (S10=YES), then the process ends. However, if the UE tries and
fails to connect to the selected PLMNID (S10=NO), the UE, in step S11,
shall remove such PLMNID from {PLMNi} and {PLMNn} sets and go back to
step S3 to perform a PLMN selection for simultaneous access with the
modified set of PLMNIDs.

[0041] In one embodiment, {PLMNn} may additionally include PLMNIDs that
have an entry in the PLMN list stored in the SIM/USIM for already
connected access technology types for which PLMN re-selection are allowed
while connected. Also, {PLMNn} may include PLMNIDs that have an entry in
the PLMN list stored in the SIM/USIM for currently not connected access
technology types for which PLMN selection for simultaneous access is
allowed.

[0042] The access technology types may include currently connected access
technology types for which PLMN re-selection is allowed. Further,
currently not connected access technology types shall be taken into
account in the PLMN selection for simultaneous access.

[0043] In one embodiment, operator policies 1 can be as follows. In
operator policy 1, PLMN re-selection on an access technology type cannot
be triggered as a result of PLMN selection on a different access
technology type. In operator policy 2, only connected access technology
types are taken into account in PLMN selection for simultaneous access.
In this embodiment, the UE can select from access technology types that
already connected.

[0044] Some use cases, in accordance with this embodiment, are presented
and shown in FIG. 5. These use cases cannot be supported without this
invention. For example, when the terminal is connected through a 3GPP
access to PLMN1 and through a WLAN access to PLMN2, the operator of PLMN1
cannot request or require the UE to offload traffic to WLAN, as it would
be offloading traffic to a different operator. However, if the inventive
method were used, and the terminal or UE were capable of connecting to
PLMN1 through WLAN access, the operator of PLMN1 would be able to offload
traffic to WLAN.

[0045] Use Cases 1.1-1.4 shown in FIG. 5 illustrate UE having PLMN
preferred list for 3GPP accesses as shown. UE is at a location where it
does not have coverage for access technology type 1 (A1) from PLMN1 but
it has coverage from PLMN3; therefore UE selects PLMN3 for A1 coverage.
For A2 in the PLMN preferred list, PLMN1 has preference over PLMN3. UE is
at a location where it has coverage for A2 from PLMN1 and from PLMN3 so
the UE selects PLMN1 for A2 access. Neither visited PLMN1 nor visited
PLMN2 can control traffic flow steering as the UE is connected to two
different PLMNs.

[0046] In particular, in Use Case 1.1 there is no overlap between A1 and
A2. UE is registered in PLMN3 through A3. Accordingly, using standard
procedures such as priority information, since PLMN1 is the highest
priority for A1, A1 is selected.

[0047] In Use Case 1.2, it is assumed that PLMN2 was not available when
the UE originally connected with A2, but PLMN2 is now available. Hence
there is overlap between A1 and A2 but UE is currently registered with
PLMN3. In this case, UE continues with PLMN3 and adds PLMN1, maintaining
stability and not forcing a change in PLMN. Instead, as shown in this use
case, the number of changes is minimized.

[0048] In Use Case 1.3, there is overlap between A1 and A2 and UE is
registered to PLMN1. Thus the intersection of PLMNi and PLMNn is PLMN1
which is selected. This is known as the "well behaved" case.

[0049] In Use Case 1.4, the UE is connected to two PLMNs, PLMN1 through A2
and PLMN2 through A3. Here, PLMN2 is selected because it provides access
to a larger number of access technologies.

[0050] In another embodiment, operator policies 1 can be as follows. In
operator policy 1, PLMN re-selection on an access technology type can
always be triggered as a result of PLMN selection on a different access
technology type. In operation policy 2, only connected access technology
types are taken into account in PLMN selection for simultaneous access.
In this embodiment, {PLMNn} additionally contains PLMNIDs that have an
entry in the PLMN list stored in the SIM/USIM for already connected
access technology types. Further, the UE can select from access
technology types that already connected.

[0051] Use Cases 2.1-2.4, shown in FIG. 6, illustrate the operator
policies of this embodiment. In Use Case 2.1, {PLMNn} contains both PLMN3
and PLMN5. UE is registered in PLMN3 through A3. However, there is no
overlap between PLMNi and PLMNn so, using standard procedures, A1
connects to PLMN1 which has the highest priority for A1.

[0052] In Use Case 2.2, the overlap of PLMNi and PLMNn is PLMN2, so that
the UE selects PLMN2. In this case, UE is registered in PLMN3 through A2
but to maintain stability, PLMN3 is not dropped when PLMN2 is added.

[0053] In Use Case 2.3, the overlap of PLMNi and PLMNn is both PLMN1 and
PLMN2. UE selects PLMN1 because it has the highest priority and UE is
already registered in PLMN1.

[0054] In Use Case 2.4, the overlap of PLMNi and PLMNn is also both PLMN1
and PLMN2. In this case, however, UE selects PLMN2 because it provides
access to a larger number of access technologies.

[0055] In yet another embodiment, operator policies can be as follows. In
operator policy 1, PLMN re-selection on an access technology type can
always be triggered as a result of PLMN selection on a different access
technology type. In operator policy 2, a specific subset of non connected
access technology types is taken into account for PLMN selection for
simultaneous access. {PLMNn} additionally contains PLMNIDs that have an
entry in the PLMN list stored in the SIM/USIM for already connected
access technology types. Further, the access technology types are those
already connected and those considered as part of operator policy 2.

[0056] The inventive technology advantageously enables accounting and
charging to be simplified. If the UE is connected to a single PLMN and
mobility between accesses is allowed, accounting is much simpler than
when the UE is connected to multiple PLMNs.

[0057] Various aspects of the present disclosure may be embodied as a
program, software, or computer instructions embodied or stored in a
computer or machine usable or readable medium, which causes the computer
or machine to perform the steps of the method when executed on the
computer, processor, and/or machine. A program storage device readable by
a machine, e.g., a computer readable medium, tangibly embodying a program
of instructions executable by the machine to perform various
functionalities and methods described in the present disclosure is also
provided.

[0058] The system and method of the present disclosure may be implemented
and run on a general-purpose computer or special-purpose computer system.
The computer system may be any type of known or will be known systems and
may typically include a processor, memory device, a storage device,
input/output devices, internal buses, and/or a communications interface
for communicating with other computer systems in conjunction with
communication hardware and software, etc.

[0059] The computer readable medium could be a computer readable storage
medium or a computer readable signal medium. Regarding a computer
readable storage medium, it may be, for example, a magnetic, optical,
electronic, electromagnetic, infrared, or semiconductor system,
apparatus, or device, or any suitable combination of the foregoing;
however, the computer readable storage medium is not limited to these
examples. Additional particular examples of the computer readable storage
medium can include: a portable computer diskette, a hard disk, a magnetic
storage device, a portable compact disc read-only memory (CD-ROM), a
random access memory (RAM), a read-only memory (ROM), an erasable
programmable read-only memory (EPROM or Flash memory), an electrical
connection having one or more wires, an optical fiber, an optical storage
device, or any appropriate combination of the foregoing; however, the
computer readable storage medium is also not limited to these examples.
Any tangible medium that can contain, or store a program for use by or in
connection with an instruction execution system, apparatus, or device
could be a computer readable storage medium.

[0060] The terms "computer system" and "computer network" as may be used
in the present application may include a variety of combinations of fixed
and/or portable computer hardware, software, peripherals, and storage
devices. The computer system may include a plurality of individual
components that are networked or otherwise linked to perform
collaboratively, or may include one or more stand-alone components. The
hardware and software components of the computer system of the present
application may include and may be included within fixed and portable
devices such as desktop, laptop, and/or server. A module may be a
component of a device, software, program, or system that implements some
"functionality", which can be embodied as software, hardware, firmware,
electronic circuitry, or etc.

[0061] The embodiments described above are illustrative examples and it
should not be construed that the present invention is limited to these
particular embodiments. Thus, various changes and modifications may be
effected by one skilled in the art without departing from the spirit or
scope of the invention as defined in the appended claims.

Patent applications by Subir Das, Belle Mead, NJ US

Patent applications by KABUSHIKI KAISHA TOSHIBA

Patent applications by TELCORDIA TECHNOLOGIES, INC.

Patent applications in class Bypass an inoperative switch or inoperative element of a switching system

Patent applications in all subclasses Bypass an inoperative switch or inoperative element of a switching system